Air-cushion vehicle edge skirt arrangement

ABSTRACT

An air-cushion vehicle lower-edge skirt arrangement including a flexible diaphragm attached at the edge of the hard structure of the vehicle and extending downwardly to an elongated member which may be substantially rigid and inclines to a lower portion beneath the hard structure, which portion may be horizontal for use at side edges or upwardly curved when at the rearward end of the vehicle, the elongated portion of the skirt being attached to the structure of the craft by diaphragms or by tie lines, the latter forming with the skirt the effect of a parallelogram, so that when the skirt moves its motion is stable and it may shift outwardly to avoid the hard structure of the craft upon extreme increments of movement. A flange or second skirt stage along the lower edge of the skirt, vent openings in the bottom of the skirt, or both, restrict the lateral side flow of air beneath the skirt. A member may be included at the top of the diaphragm to raise and lower it in controlling the attitude of the vehicle and optionally providing for side thrust or a damping effect. The diaphragm of the rearward skirt is controllable in dimension to raise and lower the skirt. Air passageways from the lift chamber may be included to inflate the skirt interiors, or the skirts may be inflated by an auxiliary blower to a pressure greater than that of the lift chamber. The vent openings may include slots that are inclined inwardly as well as downwardly, while horizontal portions of the skirts may be deflectable to increase the size of the slots. Also, there may be provided a generally horizontal panel extending across and from one end to the other of the lift chamber, the panel being pivotal about a transverse axis to vary the size of the opening to the space beneath it at the forward and rearward ends, thereby to control the amount and direction of thrust on the vehicle.

United States Patent 1191 J ackes 1451 Apr. 23, 1974 AIR-CUSHION VEHICLEEDGE SKIRT ARRANGEMENT [76] Inventor: Arthur M. Jackes, 11071 ArroyoAve., Santa Ana, Calif. 92705 22 Filed: Aug. 5, 1971 21 Appl.N0.:169,325

[52] U.S. Cl 180/128, 180/124, 180/125, 180/120 [51] Int. Cl. B60v 1/02,860v 1/16 [58] Field of Search 180/116, 127, 128, 117,l80/118,l19,120,121,122

[56] References Cited UNITED STATES PATENTS 3,363,717 l/1968 Hunt180/128 3,291,237 12/1966 Hopkins et a1 180/127 3,318,404 5/l967 Hopkinset al..... 180/128 3,414,077 12/1968 Earl 180/128 3,258,080 6/1966Williams et al.... 180/127 3,478,836 11/1969 Eckered et al..,.. 180/1283,268,021 8/1966 Jones et al. 180/128 3,500,947 3/1970 Cockerell....180/116 3,643,758 2/1972 Winter 180/128 3,536,156 10/1970 Crago 180/1283,536,154 10/1970 Faure 180/116 3,291,238 12/1966 Eggington 180/1283,244,245 4/1966 Page et al. 180/128 FOREIGN PATENTS OR APPLICATIONS1,203,025 8/1970 Great Britain 180/1 16 1,114,822 5/1968 Great Britain180/128 1,028,045 5/1966 Great Britain 180/128 Primary Examiner-DavidSchonberg Assistant Examiner.lohn P. Silverstrim Attorney, Agent, orFirm-Gausewitz, Carr & Rothenberg [5 7 ABSTRACT An air-cushion vehiclelower-edge skirt arrangement including a flexible diaphragm attached atthe edge of the hard structure of the vehicle and extending downwardlyto an elongated member which may be substantially rigid and inclines toa lower portion beneath the hard structure, which portion may behorizontal for use at side edges or upwardly curved when at the rearwardend of the vehicle, the elongated portion of the skirt being attached tothe structure of the craft by diaphragms or by tie lines, the latterforming with the skirt the effect of a parallelogram, so that when theskirt moves its motion is stable and it may shift outwardly to avoid thehard structure of the craft upon extreme increments of movement. Aflange or second skirt stage along the lower edge of the skirt, ventopenings in the bottom of the skirt, or both, restrict the lateral sideflow of air beneath the skirt. A member may be included at the top ofthe diaphragm to raise and lower it in controlling the attitude of thevehicle and optionally providing for side thrust or a damping effect.The diaphragm of the rearward skirt is controllable in dimension toraise and lower the skirt. Air passageways from the lift chamber may beincluded to inflate the skirt interiors, or the skirts may be inflatedby an auxiliary blower to a pressure greater than that of the liftchamber. The ventopenings may include slots that are inclined inwardlyas well as downwardly, while horizontal portions of the skirts may bedeflectable to increase the size of the slots. Also, there may beprovided a generally horizontal panel extending across and from one endto the other of the lift chamber, the panel being pivotal about atransverse axis to vary the size of the opening to the space beneath itat the forward and rearward ends, thereby to control the amount anddirection of thrust on the vehicle.

22 Claims, 20 Drawing Figures m m'gn APR 23 1974' SHEET 1 BF 7 /\\mw m m7 l RM w 7? 5. J@ M m ,2 4 mm. N! .M Wm

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ARTHUR M JACKES PATE E SHEET 3 [1F 7 \NVENTOR ARTHUR M. JACKES ATToiaNEY PATENTEBAPR 23 IBM 3,805,913

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ARTHUR M. JACK ATTORNEKS PATENTED m 2 3 1924 SHEET 8 OF 7 O 9 in s4- k\OZ 95 \Oil m\wzv///// /m\\\1 INVENTOR.

ARTHUR M- JACKES PATENTED PRZ I514 3.805813 SHEET 7 [1F 7 I mvewrogARTHUR -N\. JACKES BY a AIR-CUSHION VEHICLE EDGE SKIRT ARRANGEMENTBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionpertains to a skirt for an air-cushion vehicle.

2. Description of Prior Art In an air-cushion vehicle, its performanceand efficiency are affected materially by the configuration of the loweredge portions of the vehicle around the lift chamber. This part of thevehicle is subject to contact with objects beneath it, which can resultin substantial wear or damage to the elements at the lower edge of thecraft as well as rubbing drag. Rigid structural members of greaterdurability do not provide an acceptable solution because of the obviousundesirable weight penalty, the fact that wear and damage cannot beentirely eliminated in this manner and that contact with objects beneaththe craft actually can interfere with its progress. In US. Pat. No.3,486,577, there are shown skirt devices for the edge portions of anair-cushion vehicle, which are rotatably mounted and intended to pivotout of the way when there is a pressure increase beneath them because ofobstacles approached by the craft. However, in this instance and inothers in the prior art, the edge portions of the vehicle have notcombined all the needed features of light weight, simplicity and anability to avoid obstructions by being sensitive to the approach ofobstacles and automatically capable of large increments of movement toavoid contact. Also, the skirt device should present a smooth andstreamlined surface to the flow of free air around the outside of thevehicle in order to reduce air drag due to the external air flow. Hence,it is preferred that the skirt be straight rather than convoluted alongthe sides. Efficient vehicle performance also requires minimum air lossfrom the lift chamber from lateral flow beneath the side edges. At therear of the vehicle, where the discharging air creates a propulsivethrust, the outward airflow should be enhanced.

SUMMARY OF THE INVENTION The present invention provides improved skirtarrangements for the lower side edges of air-cushion vehicles, whichovercome the difficulties outlined above. The skirt includes a flexiblediaphragm attached to the outer edge of the hard structure of the craft,with a substantially rigid but flexible member inclining downwardly fromthe diaphragm to a location within the lift chamber. The degree ofrigidity, unless otherwise restrained as will be described, should besufficient to withstand cushion pressure without substantial deflection,so that the edge will remain substantially straight and smooth ratherthan bowed or wavy between restraints. The rigid member should also bemade of wear and abrasion resistant material. Tie lines extend inwardlyto hold the skirt in equilibrium as it is pressurized with air fromwithin the lift chamber. The substantially rigid lower portion of theskirt may include a horizontal section that connects to the inclinedportion. The tie lines extend between the rigid member and the hardstructure of the craft. When the horizontal section is used, the tielines are arranged so that, together with their attachments, they definesubstantially a parallelogram. Alternative to the substantially rigidskirt memher, an entirely flexible sheet may be used, with additionallines being included to confine it to the desired shape when it is underpressure, including a straight rather than bulging or wavy section alongthe side.

Normally, the horizontal section of the skirt experiences a pressurebeneath it which is less than the pressure within the lift chamber butgreater than ambient pressure. When an obstacle is encountered, thepressure beneath the rigid plate increases, causing the skirt to liftautomatically over the obstruction. The parallelogram attachment of thetie lines results in a stable lifting motion for the skirt withoutsubstantial rotation. The tie lines are positioned and of a lengthsufficient to permit the skirt to rise upwardly and outwardly of theedge of the hard structure of the vehicle, so that an obstacle may benegotiated which is as high as the hard structure is above the skirtsnormal position.

A flange depends from the lower edge of the skirt to constrict the flowof air from within the lift chamber so as to conserve it and to producethe desired pressure beneath the lower rigid element of the skirt.Alternatively, vents are provided through the skirt to result indownward air jets which likewise restrictthe lateral flow of air. Boththe flange or second skirt stage and the vents may be used if desired.

Several of the skirts may be mounted independently in end-to-endrelationship so that they may move individually in negotiatingobstructions. When the skirt is attached to a pivotal mounting plate atthe upper end of the diaphragm, it may be controlled in its verticalposition for use in raising or lowering the side of the vehicle. Also,the control plate may provide for a lateral air exhaust to produce alateral thrust on the vehicle. Alternatively, when side thrust is notneeded, the air may be confined by an auxiliary diaphragm that preventsthe lateral airflow.'The entrapped air can provide a damping effect topreclude rapid skirt position cycling due to pressure fluctuations.

Instead of tie lines, additional diaphragms may be used to connect theinner edges of the skirts to the craft, in which event the skirts arepressurized by an auxiliary blower or by openings connecting to the liftchamber. Also, inclined slots may be employed as the vents in theskirts, resulting in inwardly inclined air jets that efficiently confinethe air in the lift chamber. When the air inflating the skirts isprovided by an auxiliary blower, it may be at higher pressure than thatof the lift chamber, increasing the effectiveness of the peripheraldownward jet of air, so that the craft achieves the characteristics ofan annular jet air-cushion vehicle. Unlike conventional designs,however, stability is achieved through the action of the skirts,eliminating the requirement for a center divider or jet for stability.When the air for inflating the skirts comes from the lift chamber,variable closure means, such as movable vanes, may be used forcontrolling the access to the skirts at either the forward or therearward portion of the vehicle. This, in turn, enables the skirtpressurizing air to produce either forward or rearward thrust upon itsdischarge.

Thrust control is realized by controlling flow about a horizontaldivider panel which is pivotal about a transverse axis and extends fromone side to the other and substantially the full length of the liftchamber. In the neutral position, the panel is positioned so that accessto the space beneath it is provided around both the leading and trailingedges equally, so that the thrust is essentially zero. When the frontend of the panel is raised, the forward access to the space beneath itis increased, while the rearward access is decreased. Air introducedthrough the forward access accelerates and flows rearwardly to make upfor the reduced flow from the rear access, and thus forward thrust isproduced on the vehicle. The flow around this plate may be controlled bymeans of variable closures at the leading and trailing edges, or byvariation of plate inclination. The length of the panel may also bevariable for further controlling the amount of air which is to beallowed to flow beneath the panel. As subsequently described, theinclination of the divider panel helps to maintain uniform velocity inthe flow of air under the panel, thus enhancing efficiency.

The skirt also may be provided with a deflectable horizontal portionwhich is used to increase the size of the downwardly and inwardlydirected jet of air from within the skirts, thereby governing the amountof pressure experienced beneath the skirt. The pivotal horizontalportion may be rotatable about either its inner or its outer edge toachieve desired control functions.

I thrust on the vehicle. The rearward skirt provides a smooth contourthat offers low resistance to the flow of air which at that location isused to produce thrust for the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview, partially in elevation, of an air-cushion vehicle utilizing theinvention;

FIG. 2 is an enlarged sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a fragmentary sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a perspective view of one of the skirt assemblies;

FIG. 5 is a view similar to FIG. 2 ofa modified form of the invention inwhich all portions of the skirt are flexible;

FIG. 6 is a sectional view showing a skirt which is controllable inposition and produces a lateral side thrust when lowered;

FIG. 7 is a view of a skirt similar to that of FIG. 6, but whichprevents lateral side thrust;

FIG. 8 is a sectional view of a simplified form of skirt;

FIG. 9 is an enlarged sectional view of the skirt at the rearward end ofthe vehicle;

FIG. 10 is a bottom plan view of a modified form of the invention;

FIG. 11 is a longitudinal sectional view taken along line 11-11 of FIG.10;

FIG. 14 is an enlarged sectional view illustrating the vanes for openingand closing the forward opening to the skirts;

FIG. 15 is a bottom plan view of a different embodiment including anarrangement for controlling roll attitude and side force;

FIG. 16 is a longitudinal sectional view taken along line 16-16 of FIG.15;

FIG. 17 is a transverse sectional view of a modified skirt having anindependently movable horizontal portion;

FIG. 18 is a sectional view taken along line 18-18 of FIG. 17;

FIG. 19 is a fragmentary transverse sectional view of an arrangementsimilar to that of FIGS. 17 and 18, but with the horizontal portionhinged at the opposite side; and

FIG. 20 is a sectional view taken along line 20-20 of FIG. 19.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention provides a skirtarrangement for use on virtually any type of air-cushion vehicle. Asshown in FIG. 1, the invention is incorporated in a vehicle 10 of thegeneral type illustrated in U.S. Pat. No. 3,486,577, which includes asuitable passenger compartment 1 I mounted on a chamber 13 having anopening 14 in its forward end within which is a strut 15 that carries anengine 16 for operating a propeller 17. Air is drawn into the chamber 13by the propeller 17, providing the cushion that supports the vehicle.Along the lower portion of either side of the vehicle 10, and extendinglongitudinally within the chamber 13, is a float l8 or other hardstructure. Beneath the float 18 are skirt assemblies 19 that define thebottom edges of the chamber 13. In the embodiment illustrated, there arethree of the skirt assemblies along either side of the vehicle 10. 7

With reference to FIGS. 2, 3 and 4, each skirt assembly 19 includes aplate 21 of a rigid but yieldable material, such as a suitable plasticor rubber, that extends the length of the skirt assembly 19. The plate21 includes a normally horizontal portion 22, which connects to anupwardly inclined portion 23 that is at an obtuse angle with respect tothe section 22. The inner edge of the horizontal plate portion 22 iswithin the lift chamber 13, being underneath the float 18. A narrowdownwardly projecting flange 24 is included at the juncture between thesections 22 and 23 of the plate 21. Also, there are slots 25 in thehorizontal portion 22 of the plate 21, which extend longitudinally forsubstantially the full length of the plate 21.

Joined to the upper edge of the inclined portion 23 of the plate 21 is aflexible diaphragm 27 which connects at its upper edge to the lowerouter corner 28 of the float 18. The diaphragm 27, which is imperviousto the passage of air, extends the full length of the skirt assembly 19.At either end of the skirt assembly, connecting to the edges of theplate 21 and the diaphragm 27, are additional diaphragms 29. These serveas air barriers closing off the end portions of the skirt assembly 19 sothat it defines a chamber which is open inwardly toward the lift chamber13 of the vehicle 10.

Adjacent either end of the skirt assembly 19 or at appropriate pointsalong the length of the skirt assembly are two cables or chords 30 and31, which extend between the horizontal undersurface 32 of the float 18and the plate 21. The line 30 connects at one end to the horizontalportion 22 of the plate 21 and at its other to a point 33 on theundersurface 32 of the float 18. The other line 31 connects to theinclined portion 23 of the plate 21 and extends to a point 34 on theundersurface 32 of the float 18, which is outwardly of the point 33. Theconnections are made so that the lines 30 and 31 are substantiallyparallel.

Instead of the tie lines 30 and 31, the end diaphragms 29 may beextended and attached to the surface 32 of the float 18 at one point.(Attachment at more than one point will tend to restrict free motion ofthe assembly.) In that event, the end diaphragms serve both to retainair and to attach the skirt to the vehicle.

When the vehicle is in operation, the air from within the chamber 13 hasaccess to the skirt assemblies 19 through their open inner sides andpressurizes the interior of each skirt assembly. This causes thediaphragm to assume the arcuate configuration shown in FIGS. 2 and 4.The pressure from within the lift chamber exerts a downward and outwardforce on the plate 21, which is opposed by the lines 30 and 31 and thediaphragm 27. Lines 30 and 31 are in tension as shown, because thehorizontal plate portion 22 extends into the lift chamber 13. The airpressure holds the plate 21 normally in equilibrium in the positionshown in FIG. 2. Structural requirements are minimal for the lightweightskirt assembly 19. The plate elements 21 are continuous and have closelyspaced supports to reduce the structural loads. The skirt assembly issupported from the vehicle by tension elements, and positioned by airpressure plus these restraints.

The skirt assemblies 19 are close to each other at their ends, so thatthere is virtually no leakage between them. The end diaphragms 29 arebulged outwardly from the air pressure from within the skirt assemblies19, which helps seal the space between the adjacent skirt assemblies.

The depending flange 24 at the outer edge of the horizontal section 22of the plate 21 restricts the flow of air from within the chamber 13between the plate and the surface 36 beneath the craft. As a result, apressure lowerthan that in the lift chamber 13, but greater than ambientpressure, is experienced on the bottom of the horizontal section 22 ofthe plate 21. The slots in the plate section 22 have a similar effect.Jets of air flow downwardly from within the skirt through the slots 25,thereby providing a restriction in the passageway between the platesection 22 and the surface 36 beneath the vehicle. The restrictioneffected by these air jets likewise results in pressure greater thanambient in the space beneath the plate section 22. The pressure underplate section 22 rises or falls as the craft edge approaches or risesfrom the surface 36, creating forces and moments on the craft throughthe forces in the tie lines and 31, thus tending to stabilize craftattitude and altitude.

When an object at a higher elevation than the surface 36 is approached,the space outwardly of or beneath the skirt assembly becomescorrespondingly reduced. This, in turn, further restricts the lateraloutward flow of air from the lift chamber 13. Consequently, as the flowvelocity diminishes, the pressure beneath the horizontal plate section22 is increased. This higher pressure causes the plate 21 to be liftedupwardly, thereby avoiding the object beneath it. The skirt assembliesl9 are not connected to each other, so they may move independently asobstacles are encountered, each automatically lifting upwardly to avoidcontact.

When such lifting movement is imparted to the skirt assembly 19, theplate 21 moves in a stable manner by virtue of the nature of itsattachment to the hard structure of the craft. The tie lines 30 and 31,together with the portion of the lateral surface 32 of the float 18between the points 33 and 34, and the central portion of the plate 21,form an approximate parallelogram. As a result, the plate 21 movesupwardly and outwardly from the increased pressure beneath it, butexperiences very little rotation. In other words, the bottom portion 22of the plate 21 remains approximately parallel to the undersurface 32 ofthe float 18. Therefore, the skirt lifts in a controlled and stablemanner.

When the vehicle passes over a large obstacle, the pressure beneath theplate section 22 becomes nearly equal to that within the lift chamber13. The plate 21 then will move even further upwardly. The lengths ofthe tie lines 30 and 31 and their points of attachment to the float 18are such that the plate 21 may move to the level of the float 18,clearing it to the outside. Thus, as shown in phantom in FIG. 2, whenthe plate 21 is elevated from a large pressure rise beneath it, theinner edge 37 of the lower plate section 22 is spaced just outside thebottom inside corner 28 of the float 18. Therefore, the skirt assembly19 can pass over an object as high as the float 18 without damage,automatically shifting out of the way as the object is approached.

While the flexible portions of the skirt assembly 19 may tend tocollapse toward the upper extreme position of the skirt, it willreinflate immediately and assume its normal position as the obstructionis passed. The inflation of the skirt assembly may be augmented by apassageway 38 which conducts air from the interior of the lift chamber13 through the float 18 to an outlet opening 39 adjacent the upper endof the diaphragm 27. The air is directed downwardly adjacent the upperedge of the diaphragm 27 and will rapidly pressurize the interior of theskirt assembly 19.

With the slots 25 in the plate section 22 and the depending flange 24being ,for the same purpose in restricting the lateral airflow, it maybe possible to employ only one or the other in a given air-cushionvehicle in obtaining satisfactory results. By extending below the levelof the skirt, the flange 24 occasionally may strike some objects beneaththe craft, such as a narrow upwardly protruding element of a lateraldimension insufficient to result in the generation of sufficientpressure to lift the skirt assembly 19 an adequate distance to clear it.Consequently, there is some vulnerability to damage on the part of theflange 24, although it can at the same time offer a measure ofprotection to the plate 21. The slots 25, in providing a second path forthe escape of air from the lift chamber, prevent extreme pressurefluctuations on the plate 21. As a result, the slots 25 have a dampingeffect on vertical oscillations from cyclic pressure forces on the plate21. Downward jets along the side of the craft produced because of theslots 25 present a barrier that reduces the total air leakage from thelift chamber 13 and thereby increase efficiency of the vehicle. On theother hand, the strength of the plate 21 necessarily is reduced by thepresence of the slots 25, so that, in some instances, the inclusion ofsuch slots may be undesirable.

Similar results can be obtained from the embodiment shown in FIG. 5, inwhich the plate portion of the skirt is an entirely flexible section 40beneath the diaphragm 41. In this instance, short parallel tie lines 42on one side and 43 on the other connect from the flexible element 40 toan intermediate tie line 44. The outer main tie line 45 from the float18 connects to the upper end of the intermediate tie line 44. The otherprincipal tie line 46 extends from the float 18 to the inner portion ofthe flexible element 40. The air that inflates the skirt assembly ofFIG. 5 creates internal pressures which are opposed by the lines 42, 43and 44, as well as the principal tie lines 45 and 46. This enables theelement 40 to retain substantially the same shape as the plate 21 whileoperating in a similar manner. A slot 47 in the lower horizontal portionof the element 40 provides the downward jet of air to serve the samepurpose as the slots in the previously described embodiment.

- The version of FIG. 5 is very light in weight, possessing a lowinertia which makes it particularly sensitive to pressure variationsbeneath it. The quick response of this embodiment of the skirt makes itespecially desirable on highspeed craft.

In the arrangement of FIG. 6, the skirt assembly can be moved up anddown in controlling the attitude of the vehicle. Moving a skirt assemblydownwardly reduces the lateral airflow beneath it and so increases thepressure below the skirt. Therefore, if the skirts 19 are moveddownwardly on one side of the vehicle, that side will be raised.Conversely, upward movement lowers the vehicle on the side where suchmovement has taken place.

In the construction of FIG. 6, there is an upper horizontal plate orequivalent structure 48 which by a longitudinal shaft 49 is pivotallyconnected to a float 50 that extends along the edge of an air-cushionvehicle. The undersurface 51 of the float 50 is inclined upwardly to itsouter edge to accommodate movement of the plate 48. A crank arm 52extends from the shaft 49 and is connected to a vertically movable rod53. Therefore, movement of the rod 53 rotates the crank 52, which,.inturn, pivots the plate 48.

There is an upwardly extending flange 54 at the outer edge of the plate48, which can overlap a stepped-in surface 55 of the float when theplate 48 is pivoted upwardly. An opening 56 through the plate 48provides communication with the space between the float 50 and the plate48. The flange 54 is made to seal at the float surface 55, so thatnormally the air is retained between the float 50 and plate 48.

A skirt assembly 19 is carried beneath the plate 48, with theupper edgeof the diaphragm 27 being connected to the plate 48 at its outer edge. Atube 57 may be included along the lower surface of the plate 48 to servea purpose similar to that of the passageway 38 of the embodiment of FIG.2 in effecting inflation of the skirt 19. In addition, a spring 58 ispositioned between the upper surface of the plate 48 and theundersurface 51 of the float to maintain the plate 48 normally in thehorizontal position shown, which locates the skirt assembly 19 at itsnormal height. The force of the spring 58 is overcome readily when theskirt is to be lowered or raised.

When the plate 48 is pivoted downwardly in dropping the skirt 19, airmay escape through the opening 56 to discharge laterally above theflange 54. The result is a side thrust on the vehicle. The control ofthe skirt assembly in raising the side of the vehicle, therefore,automatically generates a side thrust to effect lateral motion of thevehicle. Moving the plate 48 back to a raised position stops the lateralair discharge and terminates the side thrust.

While the production of a lateral force often is a desirable feature, itmay be preferred to manipulate the skirt assemblies without producingthe side thrust. In some cases, only a few of several controllableskirts need provide for the side thrust. The lateral air discharge maybe eliminated by providing a diaphragm 60, as seen in FIG. 7, betweenthe outer end of the horizontal plate 48 and the outer surface of thefloat 50. The diaphragm provides a seal that will not allow air todischarge laterally even when the plate 48 is dropped downwardly amaximum distance. The diaphragm 60v is of sufficient width to permit thefull range of downward movement of the plate 48. When the opening 56 isdimensioned to provide restricted access to the space between the plate48 and the float 50, a dashpot effect can be realized to damp outfluctuations due to rapid pressure fluctuations on the skirt 19. The airin the space between the plate 48 and the float 50 is enclosed exceptfor the opening 56, and will become compressed when the plate movesupwardly rapidly. The result is a damping of undesired oscillation ofthe skirt 19.

FIG. 7 also illustrates replacement of depending flange 24 by a secondand smaller flexible skirt assembly 59. This smaller skirt assembly 59may be generally similar to the previously described arrangements, or,as shown, it may be of a somewhat simpler type, described below in moredetail with respect to FIG. 8. Thus, a two-stage skirt is obtained whichmay be used to increase skirt depth (or hard structure clearance of thesurface) more than would otherwise be possible. The two-stage skirt mayalso serve to minimize air leakage, or to improve the ride quality. Thefirst and second stage skirts will ordinarily have different dynamiccharacteristics due to differing length, size and weight, and evendifferent air pressure. This can be used to advantage to change thenatural frequency of the system, and to provide a superior suspensionsystem. The second skirt may be used where the primary skirt is attacheddirectly or otherwise to the hard structure of the craft, not beinglimited to a construction that includes the plate 48 as shown in FIG. 7.

In FIG. 8 there is illustrated a skirt 61 having an upper diaphragm 62attached to the outer corner of the rigid float or other hard structure63 of the craft, while a plate 64 of generally rigid material inclinesdownwardly from the end of the diaphragm 62. The lower end of the plate64 is beneath the float 63, so that the skirt 61 is subjected todownward pressure from the lift chamber. A tie line 65 with auxiliarylines 66 and 67 connect the plate 64 with inner portions of the float63. The skirt assembly is inflated generally as in the previouslydescribed embodiment. However, by eliminating the bottom horizontalportion of the rigid plate found in the embodiment of FIG. 2, it becomesrelatively insensitive to irregularities beneath it and lacks much ofthe self-lifting characteristic of the previously described designs.However, it is a simple construction and operates well over smoothsurfaces. In this arrangement, there is shown an air passsage 68 throughthe hard structure 63 to introduce air into the skirt assembly 61 in theevent that it should become collapsed from contact with an object below.

A vane 69 may be included, if desired, at the inner edge of the hardstructure 63, this vane extending longitudinally and being inclinedoutwardly and downwardly toward the skirt assembly 61. The vane 69,therefore, directs air from the interior of the lift chamber into theskirt assembly. When the vane is included, the skirt assembly has someability to lift when obstacles are encountered because proximity to thesurface modifies the normal distribution of pressure on the skirt 61.

The skirt 7] shown in FIG. 9 is positioned at the rearward end of thelift chamber 13 of the vehicle 10. Air exhausting to the rear beneaththe skirt 71 provides forward thrust for the vehicle 10, so that it isdesirable to have a smooth contour at this location, which will minimizeresistance to the flow of the air. This is accomplished by the skirt 71,which is rounded at its lower portion and inclines upwardly at a gradualangle toward the rear.

The central portion 73 of the skirt 71 is of a rigid but yieldablematerial, such as that used for the plate 21 in the embodiment of FIGS.1-4. The member 73 extends for the full length of the skirt 7] and iscurved in one plane so as to form a shallow channel in cross section,the convex side of which faces downwardly. The rearward portion 74 ofthe skirt 71 is a flexible membrane which is impervious to the flow ofair. One edge of this membrane connects to and extends the length of thesubstantially rigid element 73, while the opposite end connects to aspool 75 rotatably mounted at the rearward end of the vehicle 10.Rotation of the spool 75 varies the width of the diaphragm 74 in eitherraising or lowering the skirt 71.

The forward part 76 of the skirt 71 may be a flexible diaphragm thatinclines upwardly and forwardly to the hard structure 77 at the rearwardend of the lift chamber 13. Suitable cables or cords attached to theforward end of the element 73 also may be used, but a solid diaphragmwill preclude scooping water or debris into the interior of the skirt71. Also, the forward portion 76 may be a rigid member which is attachedby a hinge or flexible fastening to the hard structure 77 of the craft,and by a similar connection to the forward edge of the portion 73 of theskirt 71.

A passageway 78 is provided through the hard structure of the craft intothe interior of the skirt 71. This provides communication between thelift chamber 13 and the interior of the skirt 71. As a result, the skirt71 is inflated substantially to the same pressure that exists within thelift chamber, which causes the skirt to assume the configuration shownin FIG. 9. When tie lines are used to attach the forward end of themember 73 to the vehicle, the passageway 78 is unnecessary.

The arcuate configuration of the rigid but yieldable central portion 73of the skirt 71 minimizes the deflection of the membranes 74 and 76 bythe pressure of air within the skirt 71 by increasing the tension inthese members so that they assume a relatively low curvature. Thisprovides the equivalent of an efficiently contoured nozzle at therearward end of the lift chamber. By raising or lowering the skirt 71through the operation of the spool 75, the area of the air dischargepath is controlled. This, in turn, controls the thrust on the vehicle10. Obviously, when the skirt 71 is elevated, the thrust is increased,while the skirt also may be lowered sufficiently to eliminate forwardthrust due to this noz zle action.

The skirt shown in FIGS. 10-12 includes a plate of substantially rigidbut yieldable material and an outer flexible diaphragm 82 similar to thecorresponding components of the skirt previously described. An innerlongitudinal slot 83 extends through the plate 81 at the inner edge ofthe horizontal portion 84 of the plate. The parallel outer slot 85 ispositioned at the line of connection between the horizontal portion 84and the outer sloping portion 86 of the plate 81. The outer slot 85 isinclined inwardly at the angle of the sloping portion 86 of the plate81. This means that air discharged through the outer slot 85 is directedboth downwardly and inwardly toward the lift chamber. The result is anenhanced sealing effect at the perimeter of the lift chamber to moreeffectively retain air within the lift chamber.

A diaphragm 87 extends from the inner edge of the horizontal portion 84of the plate 81 to the comer of the hard structure 88 at the edge of thecraft. This diaphragm retains the skirt, replacing the tie linespreviously described. Air for inflating the skirt 80 is supplied by anauxiliary power-driven blower 89 mounted at any convenient place on thevehicle and connected by a duct 90 to an opening 91 through the hardstructure 88, discharging into the interior of the skirt 80 adjacent thediaphragms and the plate. The air thus supplied may be at a greaterpressure than that existing within the lift chamber. This accounts forthe curvature of the diaphragm 87, as shown in FIG. 12, with a convexsurface being presented adjacent the lift chamber.

In the embodiment shown in FIGS. 10-12, there are two of the skirts 80on either side of the vehicle, collectively extending substantially thefull length of the vehicle. Similar skirts 92 are arranged to a V-shapedpattern at the bow of the craft. The skirts 80 and 92 may be providedwith end diaphragms 93 to help retain air as the skirts moveindividually, but which do not extend the full height of the skirt, sothat there is communication from one skirt to the other. This allows thepressurized air from the blower 89 or other source to supply the variousskirts.

At the rear of the vehicle, the skirt 71 of FIG. 9 is used again,allowing air to escape in the rearward direction. This is desirablebecause the rearwardly discharging air provides thrust for the vehicle.

With the skirts 80 and 92 being supplied with air at a pressure higherthan that in the lift chamber 94, the front and side flow ischaracteristic of an annular jet air-cushion vehicle. The resultingcombination of plenum and annular jet has, as a result, a lower totalairflow than the previously described embodiments. The energy of theside and front airflow cannot be completely recovered in the form ofpropulsive work. Therefore, it is usually advantageous to reduce thisairflow, which may permit a higher surface clearance to be realized thanotherwise would be possible. Substantially all of the energy of the rearflow can be recovered as propulsive work, and thus it is usually desiredto 1 I maintain a high volume of air flowing past the rear edge of thelift chamber. The flat surface of the horizontal plate 84 is sensitiveto surface proximity and so stabilizes the craft in a level attitude.Thus, if one side of the craft should drop, the pressure will increasebeneath the horizontal plate portion 84 on that side, automaticallyrighting the craft. Conversely, if one side should rise, the pressurebeneath the horizontal plate surface 84 decreases, allowing that side todrop. As a result of this self-leveling effect, there is no necessityfor a jet or an additional skirt at the centerline of the craft forstabilization, which is a significant advantage over conventionalannular jet air-cushion vehicles. The present design, therefore, has thecharacteristics of automatic stabilization of attitude, an efficientsealing of air within the lift chamber and a much larger internalairflow than in previous designs of annular jet air-cushion vehicles,which is used in flow past the rear edge for propulsion as well as lift.

The skirt 80 shown in FIGS. 10-12 may be mounted on a hinged movablestructure, such as shown in FIG. 6, to permit the skirt to be deflecteddownwardly to control the vehicle attitude. Air may be permitted toescape to the side of the craft upon this deflection, or there may be anadditional air pocket for damping oscillations, such as the type shownin FIG. 7. Variations also are possible in the design of the craft,which does not necessarily have to have a forward air inlet for the liftchamber, but which may draw air in vertically instead. Externalpropulsion means by propeller or jet may be used if desired.

A horizontal force vector control system also is provided, whichincludes a generally horizontal divider panel 95 extending across thelift chamber from one side to the other, and also divider panels 102extending across the ducts 90 which feed the annular jet side skirts 80.The action of divider panels 102 and 95 is similar in controlling boththe direction and velocity of their respective flows. In the following,for simplicity, the action of the panel 95 only will be described, butthis should describe equally the action of plates 102. The panel 95extends for substantially the full length of the lift chamber, and ispositioned below the upper wall of the lift chamber, just above theskirts 80. The panel 95 is substantially flat, but has a slight upwardcurvature at the forward end portion 96. The divider panel 95 is mountedon journals 97 so that it is pivotal about a horizontal axis transverseto the vehicle. In the example shown, there is a crank arm 98 extendingfrom the panel 95 and movable by a power cylinder 99 to accomplishrotation of the panel.

The divider panel 95 provides a means for controlling the thrust of themain body of air in the lift chamber which escapes past the rear skirt71. When the forward end 96 of the panel 95 is pivoted upwardly, asshown in FIG. 1 l, the effect is to increase the size of the opening atthe forward portion of the vehicle between the air inlet 100 and thespace beneath the panel 95,and to reduce the size of the opening betweenthe trailing edge 101 of the panel 95 and the top edge of the transverserear skirt 71. The result is that more air passes under panel 95 at thefront than at the rear. This air is accelerated in a rearward directionto replace the air formerly entering at the rear. The result is anincrease in forward thrust.

However, if the forward end 96 of the divider panel 95 is pivoteddownwardly, as shown in phantom lines in FIG. 11, the trailing edge 101becomes spaced upwardly from the top edge of the rear skirt 71. At thesame time, the forward end of the divider panel is moved into adjacencywith the transverse bottom edge 103 of the air-inlet passageway 100.This prevents air from flowing beneath the horizontal divider panel 95from the forward end. There is, however, an air path at the rear pastthe trailing edge 101. That air flows forwardly because it must replacethe air formerly introduced from the forward end. Thus, a forwardvelocity is imparted to the air, resulting in a reverse thrust on thevehicle. As a result, the panel 95 permits the vehicle to be movedbackward as well as forward. Of course, the panel 95 may be positionedintermediate these extremes to suit particular conditions.

Thrust is increased by lowering the trailing edge of divider panel 95.As this change occurs, the desired uniform pressure may be maintained bymoving the forward end portion 96 of the panel 95, which is separate,being carried on a telescoping mount 104 and engaged by a power cylinder105. This permits the forward end portion 96 of the panel to beretracted rearwardly as the power cylinder 105 is retracted. As aresult, the area of the effective opening to the space beneath the panel95 is made larger, raising the pressure at the front of the craft.Because the divider panel 95 is inclined downwardly at the rear whenforward thrust is being produced, a uniform pressure is realizedthroughout the length of the lift chamber. A small amount of air escapesto the sides as the air flows rearwardly toward the rear skirt 71. Withthe divider panel 95 being inclined downwardly toward the rear, the areabeneath it progressively becomes smaller. As a result, even though thequantity of air is reduced by the amount that escapes to the sides, thevelocity of the air can be maintained constant, and a constant pressureis realized.

By proper selection of both plate angle and the position of the frontend portion, the pressure may be maintained constant while the generaldirection of the flow is varied from neutral to rearwardly for increasedthrust. Similarly, the pressure may be maintained constant and uniformwhile the air is given a net forward direction so as to produce reversethrust.

Also, the divider panel 95 should be inclined by at least the maximumprobable pitch angle which could be experienced by the craft to avoid adestabilizing pressure on the divider panel. For example, if the vehicleis in a nose down condition, the divider panel 95 should be at least inthe horizontal position so that forces generated on the panel will notpush the nose further downwardly.

Another form of the force vector control system is shown in FIGS. 13 and14. In this arrangement, used in lieu of the annular jet skirt system ofFIGS. l012 that relies upon an auxiliary blower 89, air flows into theside skirts from the lift chamber. This flow may be controlled by thearrangement shown. The hard structure 107 shown in FIGS. 13 and 14 issimilar to the plate 95 previously described, except that it is fixed inposition. It does not extend for the full length of the side of thevehicle. Forwardly of the structure 107 is a set of parallel vanes 108,while a similar set of vanes 109 is positioned rearwardly of thestructure 107. The vanes 108 and 109 are pivotal so that they canselectively close off or open up the spaces at the forward and rearwardends of the structure 107. Any suitable means may be provided forrotating the vanes 108 and 109, such as the arrangement shown in FIG. 14for the vanes 108. In this construction, there are crank arms 110connected to the mounting shafts 111 of the vanes 108. The outer ends ofthe crank arms 1 are connected to a rod 112 that extends to a powercylinder 113 carried by the structure 107. Extension of the powercylinder 113 from the position shown in FIG. 1 1 will rotate the crankarms 110 in the counterclockwise direction as illustrated, therebyrotating the vanes 108 in the same direction to close the opening at theforward end of the structure 107.

When the front vanes 108 are open and the rearward vanes 109 are closed,air will enter at the front portion of the forward skirt 80, dischargingat the rearward end of the rearward skirt along the side of the vehicle.This air has a significant velocity through the side skirts so that, asit escapes to the rear, it produces a forward thrust component on thevehicle. This conserves the energy of the air brought into the liftchamber and contributes to the propulsive effect on the craft. This airoffsets both the external drag and also the ram drag due to capturingair in the lift chamber at the velocity of the vehicle. Of course, whenrearward thrust is to be obtained, the vanes are reversed, with theforward vanes 108 being closed and the rearward vanes 109 opened.

The vanes 108 and 109 may be extended inwardly of the side edges of thecraft so as to encompass the'full width of the lift propulsion chamber,as shown in FIGS. and 16. In this arrangement, the vanes 108 and 109 arelocated forwardly of the leading edge 96 and rearwardly of the trailingedge 101 of the panel 95. Operation of the vanes 108 and 109 controlsthe flow of air around the leading and trailing edges 96 and l0l,respectively. The pivotal mounting of the panel 95 is maintained fortrim control and to permit achieving efficient thrust. The upwardinclination of the leading edge 96 helps provide an efficientacceleration of the air as it enters the lift and thrust chamber.

In this example, the panel 95 is made in two sections 95a and 95b,separated along the longitudinal centerline of the craft. The vanes 108and 109 similarly are in two parts 108a and l08b and 109a and 109b,respectively, divided at this location. The opposite parts of the vanesand the panel 95 may be operated separately and differentially tocontrol the roll attitude and also the horizontal side force. A powercylinder 99 is included for each of the sections 95a and 95b of thepanel 95. Also, there is a power cylinder 113 for each section of thevanes 108 and of the vanes 109. With this kind of control, more air isdischarged on the high side than on the low side, but also the largermass of air is discharged at a higher side angle and a higher velocitythan the air on the low side. Thus, the side force due to roll isaugmented.

Another control arrangement is shown in FIGS. 17 and 18, in which thejet of air at the periphery of the craft may be varied. The skirt 115shown in these views is generally similar to the skirt 80 previouslydescribed, including an outer diaphragm 116 along the edge of the craftand an inner diaphragm 117 that connects to the hard structure 118. Theplate portion of the skirt includes an inclined outer part 119 and ahorizontal section 120. Unlike the skirt- 80, the skirt 1 15 includes aninner portion 121 that inclines inwardly and upwardly from the inneredge of the horizontal plate portion 120. A slot 122 is included betweenthe horizontal portion 120 and the outer inclined portion 119. Thisprovides for the outer jet of air inwardly and downwardly along theperiphery of the craft.

At the inner part of the horizontal portion 120 are intermittent slots123 which leave narrow sections 124 of the material of the plate portionof the skirt, interconnecting the inner inclined part 121 and thehorizontal portion 120. The inner vertical jet of air exhausts throughthe slots 123. The horizontal portion of the skirt is unconnected to theremainder of the skirt at its ends 125. Tie lines 126 are connected tothe horizontal skirt section 120 and provide support for this section ofthe skirt.

When the tie lines 126 are pulled upwardly, the narrow connecting strips124 will bend, allowing the section 120 of the skirt to be pivotedupwardly as if it were hinged along its inner longitudinal edge. Thisincreases the width of the outer jet slot 122, thereby allowing thedischarge of a greater quantity of air at the outer jet along the sideof the vehicle. The result is a greater lift beneath the skirt 115. Thisincrease in lift occurs because the augmented peripheral jet provides aneven greater barrier to the lateral outward flow of air from the liftchamber than that of the normal narrower jet of downwardly and inwardlyflowing air. With the increased barrier to outward flow, the lateralvelocity of the air beneath the skirt is reduced and the pressure isincreased.

The skirt sections may be controlled individually to produce rollcontrol for the craft. This is accomplished without requiring as muchdeflection of the entire skirt as would be required where the skirtassembly as a whole is deflected as described above. This arrangementalso can enhance the automatic pressure increase beneath the skirt as itapproaches the surface beneath it to assist in shifting the skirtupwardly to avoid contact. As the pressure beneath the section 120becomes greater when the surface beneath the craft is approached, theadded upward force will result in a pivoting of the section 120 as thenarrow connecting strips 124 are bent. Automatically, therefore, theouter peripheral jet will become larger to cause an increase of thepressure beneath the skirt.

The same principles may be applied in a different manner by theconstruction shown in FIGS. 19 and 20, where the horizontal portion ofthe skirt is hinged at its opposite side. Thus, as shown in thisillustration, there is an open slot 127 along the inner edge of thehorizontal portion 128 of the skirt 129. At the outer edge of thehorizontal portion 128, there is a slot 130 that is interrupted bynarrow strips 131 interconnecting the horizontal portion 128 with theouter inclined part 132 of the skirt. In this arrangement, the outerslot 130 is vertical, while the inner slot 127 is inwardly inclined.

The operation of the skirt 129 is opposite from that of the skirt 15.Thus, when the portion 128 of the skirt 129 is lifted by the tie lines133, the inner peripheral jet is increased, providing a greater barrierto the outer flow of air from the lift chamber before it reaches theintermediate portion of the skirt. This blocks the higher pressure liftchamber air from the intermediate portion of the skirt so that thepressure beneath the skirt is reduced. When there is sufficientclearance beneath the craft to assure that the skirt will not contactthe surface beneath it, this may be used in cushioning the effect ofpassing over an uneven surface. It is possible to incorporate bothskirts 115 and 129 in the same vehicle,

preferably arranged alternately so that they may be operated selectivelyto achieve desired effects.

The foregoing detailed description is to be clearly understood as givenby way of illustration and example only, the spirit and scope of thisinvention being limited solely by the appended claims.

I claim:

1. In combination with an air-cushion vehicle having a a lift chamber,means for providing pressurized air in said lift chamber, and agenerally rigid structure having a lateral surface extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber,

one longitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber,

a plate means,

said plate means including an edge connected to the lower edge of saiddiaphragm,

a first portion inclined downwardly and inwardly from said edge thereof,

and a second generally horizontal portion connected to said firstportion at an obtuse angle relative thereto, for being reacted upon bypressures above and below said second portion for moving said skirtarrangement upwardly and downwardly, said second portion being beneathsaid lateral surface, means for applying pressurized air to the uppersurface of said plate means and to said side of said flexible diaphragm,

and means interconnecting said plate means and said vehicle, said meansinterconnecting said plate means and said vehicle including a duality offlexible members, a first end of each of said flexible members beingconnected to said lateral surface, said first ends being at spacedlocations, the opposite second end of each of said flexible membersbeing connected to said plate means, said second ends being at spacedlocations,

said flexible members together with the portions of said lateral surfaceand said plate A means therebetween defining approximately aparallelogram, for thereby allowing said plate means to move outwardlyand upwardly in a stable manner relative to said lateral surface.

2. A device as recited in claim 1 in which said connections of saidfirst ends of said flexible members are such that said first end of oneof said flexible members is laterally outwardly relative to said liftchamber with respect to said first end of the other of said flexiblemembers,

said second end of said one flexible member being connected to saidfirst inclined portion of said plat means,

said second end of said other flexible member being connected to saidsecond generally horizontal portion of said plate means.

3. A device as recited in claim 1 in which said flexible members are ofan adequate length and connected to said lateral surface at positionssuch that said plate means can move upwardly to the level of saidlateral surface and simultaneously move outwardly a distance sufficientto clear said edge of said lift chamber.

4. in combination with an air-cushion vehicle having a lift chamber,means for providing pressurized air in said lift chamber, and agenerally rigid structure having a lateral surface extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber,

one longitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber,

a plate means,

said plate means including an edge connected to the lower edge of saiddipahragm,

said plate means being inclined downwardly from said edge thereof to aportion thereof which is beneath said lateral surface,

means for applying pressurized air to the upper surface of said platemeans and to said side of said flexible diaphragm,

means interconnecting said plate means and said vehicle, and means formoving said skirt arrangement downwardly relative to said lateralsurface, said means for moving said skirt arrangement downwardlyincluding movable means carried by said rigid structure at said edge ofsaid lift chamber, said one longitudinal edge of said diaphragm beingsecured to said movable means, whereby movement of said movable meansmoves said diaphragm therewith, said movable means including a generallyhorizontal member having an inner edge and an outer edge, and meanspivotally attaching said inner edge to said rigid structure-so'as toposition said generally horizontal member adjacent said lateral surfacewith said outer edge adjacent said edge of said lift chamber, said onelongitudinal edge of said diaphragm being attached to said outer edge ofsaid generally horizontal member, said generally horizontal memberhaving an opening means therethrough providing communication betweensaid lift chamber and the space between said generally horizontal memberand said lateral surface of said rigid structure.

5. A device-as recited in claim 4 including means for discharging airfrom said space laterally with respect to said vehicle uponpredetermined downward movement of said generally horizontal member, forthereby imposing a side thrust on said vehicle.

6. A device as recited in claim 5 in which for said means fordischarging air from said space laterally said generally horizontalmember includes an upstanding flange on said outer edge thereof, saidupstanding flange being normally in sealing relationship with said edgeof said lift chamber, said upstanding flange being moved to a positionwhere it is spaced downwardly from said edge of said lift chamber uponsaid predetermined downward movement of said generally horizontalmember.

7. A device as recited in claim 4 including in addition a seconddiaphragm interconnecting said outer edge of said generally horizontalmember and said edge of said lift chamber for substantially preventinglateral discharge of air from said space upon downward movement of saidgenerally horizontal member.

8. A device as recited in claim 7 in which said opening means providesrestricted communication between said lift chamber and said space,whereby air is substantially retained in said space and provides aspringlike action and a damping effect upon oscillation of saidgenerally horizontal member.

9. In combination with an air-cushion vehicle having a lift chamberhaving an open bottom, means for providing pressurized air in said liftchamber, and a generally rigid structure having a lateral surface spacedoutwardly from the center of said lift chamber and extending along anedge of said lift chamber, a skirt arrangment for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber,

one longitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber,

a plate means,

said plate means including an outer edge connected to the lower edge ofsaid diaphragm,

said plate means being inclined downwardly from said outer edge thereofto a portion thereof which is beneath said lateral surface,

said plate means including an inner edge spaced outwardly from thecenter of said lift chamber and adjacent said lateral surface forpermitting air to flow from said lift chamber generally horizontallyoutwardly under said plate means to the exterior of said lift chamber,

said plate means including a first downwardly and inwardly inclinedportion, and a second generally flat horizontal portion connected to thelower edge of said first portion at an obtuse angle relative thereto andextending inwardly therefrom to said inner edge of said plate, for beingreacted upon by pressures above and below said second portion for movingsaid skirt arrangement upwardly and downwardly,

means for applying pressurized air to the upper surface of said platemeans and to said side of said flexible diaphragm, and

flexible means interconnecting said plate means and said vehicle,

said plate means being a flexible sheet member, said meansinterconnecting said plate means and said vehicle including flexibleelements attached to said first portion and to said second portion ofsaid plate means for generally maintaining the shape of said plate meanswhen said plate means is so subjected to pressure from pressurized airin said lift chamber.

10. In combination with an air-cushion vehicle having a lift chamberhaving an open bottom, means for providing pressurized air in said liftchamber, and a generally rigid structure having a lateral surface spacedoutwardly from the center of said lift chamber and extending along anedge of said lift chamber at the rearward end thereof, a skirtarrangement for said lift chamber comprising a flexible diaphragmdisposed longitudinally of said edge so as to present one side of saiddiaphragm adjacent said lift chamber, one longitudinal edge of saiddiaphragm being attached to said vehicle adjacent said edge of said liftchamber, a plate means,

said plate means including an outer edge connected to the lower edge ofsaid diaphragm,

said plate means being included downwardly from said outer edge thereofto a portion thereof which is beneath said lateral surface,

said plate means including an inner edge spaced outwardly from thecenter of said lift chamber and adjacent said lateral surface forpermitting air to flow from said lift chamber generally horizontallyoutwardly under said plate means to the exterior of said lift chamber,

said plate means being a substantially rigid member curved to form ashallow channel with a convex surface facing downwardly,

said diaphragm being inclined downwardly and forwardly relative to saidvehicle from said attach ment thereof adjacent said edge of said liftchamber to said connection thereof to said plate means, means forapplying pressurized air to the upper surface of said plate means and tosaid side of said flexible diaphragm, and flexible means interconnectingsaid plate means and said vehicle. 11. A device as recited in claim 10including in addition means for varying the dimension of said diaphragmfor raising and lowering said plate means.

12. A device as recited in claim 11 in which said means for varying thedimension of said diaphragm includes a rotatable spool on said vehicle,said one longitudinal edge of said diaphragm being attached to saidspool.

13. A device as recited in claim 10 in which said substantially rigidmember includes a portion inclined upwardly and forwardly relative tosaid vehicle to an opposite edge thereof.

14. A device as recited in claim 10 in which said means interconnectingsaid plate means and said vehicle includes a diaphragm inclined upwardlyand forwardly from the forward edge of said substantially rigid memberto said lateral surface,

and including in addition a conduit means providing communicationbetween said lift chamber and the interior of said skirt arrangement,whereby pressurized air from said lift chamber inflates said skirtarrangement.

15. In combination with an air-cushion vehicle having a lift chamberhaving an open bott in, means for providing pressurized air in said liftamber, and a generally rigid structure having a lateral surface spacedoutwardly from the center of said lift chamber and extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber,

19 one longitudinal edge of said diaphragm being attached to saidvehicle adjacent said edge of said lift chamber,

a plate means,

said plate means including an outer edge connected to the lower edge ofsaid diaphragm,

said plate means being inclined downwardly from said outer edge thereofto a portion thereof which is beneath said lateral surface,

said plate means including an inner edge spaced outwardly from thecenter of said lift chamber and adjacent said lateral surface forpermitting air to flow from said lift chamber generally horizontallyoutwardly under said plate means to the exterior of said lift chamber,

said plate means including a first downwardly and inwardly inclinedportion, and a second generally flat horizontal portion connected to thelower edge of said first portion at an obtuse angle relative thereto andextending inwardly therefrom to said inner edge of said plate, for beingreacted upon by pressures above and below said second portion for movingsaid skirt arrangement upwardly and downwardly,

aperture means in said generally horizontal portion of said plate meansfor discharging air from said skirt arrangement in a generally downwarddirection adjacent said second portion and constricting the outwardgenerally horizontal flow of air from said lift chamber under said skirtarrangement,

said aperture means including a duality of elongated slots,

the first of said slots being adjacent the outer edge of said secondportion and being inclined downwardly and inwardly for discharging a jetof air downwardly and inwardly therefrom,

the second of said slots being inwardly of said first slot and beingsubstantially vertically oriented for discharging a jet of airvertically downwardly therefrom,

means for applying pressurized air to the upper surface of said platemeans and to said side of said flexible diaphragm,

and flexible means interconnecting said plate means and said vehicle.

16. In combination with an air-cushion vehicle having a lift chamberhaving an open bottom, means for providing pressurized air in said liftchamber, and a generally rigid structure having a lateral surface spacedoutwardly from the center of said lift chamber and extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a plurality of skirt units substantially in end-to-endalignment along said edge of said lift chamber, with the ends ofadjacent skirt units being in juxtaposition, said skirt units beingunconnected to each other so as to be independently movable, each ofsaid skirt units including a flexible diaphragm disposed longitudinallyof said edge so as to present one sideof said diaphragm adjacent saidlift chamber, one longitudinal edge of said diaphragm being attached tosaid vehicle adjacent said edge of said lift chamber, a plate means,

said plate means including an outer edge connected to the lower edge ofsaid diaphragm, said plate means being inclined downwardly from saidouter edge thereof to a portion thereof which is beneath said lateralsurface, said plate means including an inner edge spaced outwardly fromthe center of said lift chamber and adjacent said lateral surface forpermitting air to flow from said lift chamber generally horizontallyoutwardly under said plate means to the exterior of said lift chamber,means for applying pressurized air to the upper surface of said platemeans and to said side of said flexible diaphragm, flexible meansinterconnecting said plate means and said vehicle, and an additionalflexible diaphragm at either end of said skirt unit positioned at theends of said first-mentioned diaphragm and the ends of said plate means,said additional flexible diaphragms covering less than the entire spaceat the'ends of said skirt unit for allowing air to flow from one of saidskirt units to the other.

17. In combination with an air-cushion vehicle having a lift chamber,means for providing pressurized air in said lift chamber, and agenerally rigid structure having a lateral surface extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising:

a flexible diaphragm disposed longitudinally of said edge so as topresent one side of said diaphragm adjacent said lift chamber, onelongitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber,

a plate means,

said plate means including an edge connected to the lower edge of saiddiaphragm,

a first portion extending downwardly and inwardly from said edge thereofwith respect to said lift chamber,

a second generally horizontal portion beneath said lateral surfaceconnected to the lower edge of said first portion. at an obtuse anglerelative thereto and extending inwardly therefrom with respect to saidlift chamber,

and a third portion connected to the inneredge of said first portion andextending upwardly and inwardly therefrom with respect to said liftchamber,

said plate means including a duality of elongated slots, the first ofsaid slots extending longitudinally of said plate means substantially atthe connection between said first andsecond portions thereof, the secondof said slots extending longitudinally of said plate means substantiallyat the connection between said second and third portions thereof,

said second portion of said plate means being connected to said thirdportion of said plate means so as to be pivotal relative to said thirdportion of said plate means substantially about an axis extendinggenerally along the line of connection between said second and thirdportions,

said first slot being defined on one side thereof by the outer edge ofsaid second portion of said plate means,

means for so pivoting said second portion relative to said third portionfor increasing the size of said first slot, means for applyingpressurized air to the upper surface of said plate means and to saidside of said flexible diaphragm,

and means interconnecting said plate means and said vehicle,

said means interconnecting said plate means and said vehicle being asecond diaphragm,

said second diaphragm extending from said portion of said plate means tosaid generally rigid structure,

said second diaphragm being connected to the inner edge of said thirdportion of said plate means.

18. A device as recited in claim 17 in which for said connection of saidsecond portion to said third portion there are relatively narrowdeflectable strips of said plate means extending transversely acrosssaid second slot between said second and third portions of said platemeans.

19. A device as recited in claim 18 in which said first slot is inclineddownwardly and inwardly relative to said vehicle, and said second slotis substantially vertical.

20. In combination with an air-cushion vehicle having a lift chamberhaving an open bottom, means for providing pressurized air in said liftchamber, and a generally rigid structure having a lateral surface spacedoutwardly from the center of said lift chamber and extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber, 7one longitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber, a plate means,

said plate means including an outer edge connected to the lower edge ofsaid diaphragm,

said plate means being inclined downwardly from said outer edge thereofto a portion thereof which is beneath said lateral surface,

said plate means including an inner edge spaced outwardly from thecenter of said lift chamber and adjacent said lateral surface forpermitting air to flow from said lift chamber generally horizontallyoutwardly under said plate means to the exterior of said lift chamber,means for applying pressurized air to the upper surface of said platemeans and to said side of said flexible diaphragm, flexible meansinterconnecting said plate means and said vehicle, said flexible meansbeing a second diaphragm extending from said portion of said plate meansto said generally rigid structure, said plate means including a firstportion extending downwardly and inwardly with respect to said liftchamber, a second generally horizontal portion connected to the loweredge of said first portion at an obtuse angle relative thereto andextending inwardly therefrom with respect to said lift chamber, and athird portion connected to the inner edge of said first portion andextending upwardly and inwardly therefrom with respect to said liftchamber to said inner edge of said plate means, said second diaphragmbeing connected to the inner edge of said third portion of said platemeans, said plate means including a duality of elongated slots, thefirst of said slots extending longitudinally of said plate meanssubstantially at the connection between said second and third portionsthereof,

said second portion of said plate means being connected to said firstportion of said plate means so as to be pivotal relative to said firstportion of said plate means substantially about an axis extendinggenerally along the line of connection between said first and secondportions, said second slot being defined on one side thereof by theinner edge of said second portion of said plate means, and means for sopivoting said second portion relative to said first portion forincreasing the size of said second slot. 21. A device as recited inclaim 20 in which for said connection of said second portion to saidfirst portion there are relatively narrow deflectable strips of saidplate means extending transversely across said first slot between saidfirst and second portions of said plate means.

22. A device as recited in claim 21 in which said second slot isinclined downwardly and inwardly relative to said vehicle, and saidsecond slot is substantially vertical.

1. In combination with an air-cushion vehicle having a a lift chamber,means for providing pressurized air in said lift chamber, and agenerally rigid structure having a lateral surface extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber, onelongitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber, a plate means, said plate meansincluding an edge connected to the lower edge of said diaphragm, a firstportion inclined downwardly and inwardly from said edge thereof, and asecond generally horizontal portion connected to said first portion atan obtuse angle relative thereto, for being reacted upon by pressuresabove and below said second portion for moving said skirt arrangementupwardly and downwardly, said second portion being beneath said lateralsurface, means for applying pressurized air to the upper surface of saidplate means and to said side of said flexible diaphragm, and meansinterconnecting said plate means and said vehicle, said meansinterconnecting said plate means and said vehicle including a duality offlexible members, a first end of each of said flexible members beingconnected to said lateral surface, said first ends being at spacedlocations, the opposite second end of each of said flexible membersbeing connected to said plate means, said second ends being at spacedlocations, said flexible members together with the portions of saidlateral surface and said plate means therebetween defining approximatelya parallelogram, for thereby allowing said plate means to move outwardlyand upwardly in a stable manner relative to said lateral surface.
 2. Adevice as recited in claim 1 in which said connections of said firstends of said flexible members are such that said first end of one ofsaid flexible members is laterally outwardly relative to said liftchamber with respect to said first end of the other of said flexiblemembers, said second end of said one flexible member being connected tosaid first inclined portion of said plate means, said second end of saidother flexible member being connected to said second generallyhorizontal portion of said plate means.
 3. A device as recited in claim1 in which said flexible members are of an adequate length and connectedto said lateral surface at positions such that said plate means can moveupwardly to the level of said lateral surface and simultaneously moveoutwardly a distance sufficient to clear said edge of said lift chamber.4. In combination with an air-cushion vehicle having a lift chamber,means for providing pressurized air in said lift chamber, and agenerally rigid structure having a lateral surface extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber, onelongitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber, a plate means, said plate meansincluding an edge connected to the lower edge of said dipahragm, saidplate means being inclined downwardly from said edge thereof to aportion thereof which is beneath said lateral surface, means forapplying pressurized air to the upper surface of said plate means and tosaid side of said flexible diaphragm, means interconnecting said platemeans and said vehicle, and means for moving said skirt arrangementdownwardly relative to said lateral surface, said means for moving saidskirt arrangement downwardly including movable means carried by saidrigid structure at said edge of said lift chamber, said one lOngitudinaledge of said diaphragm being secured to said movable means, wherebymovement of said movable means moves said diaphragm therewith, saidmovable means including a generally horizontal member having an inneredge and an outer edge, and means pivotally attaching said inner edge tosaid rigid structure so as to position said generally horizontal memberadjacent said lateral surface with said outer edge adjacent said edge ofsaid lift chamber, said one longitudinal edge of said diaphragm beingattached to said outer edge of said generally horizontal member, saidgenerally horizontal member having an opening means therethroughproviding communication between said lift chamber and the space betweensaid generally horizontal member and said lateral surface of said rigidstructure.
 5. A device as recited in claim 4 including means fordischarging air from said space laterally with respect to said vehicleupon predetermined downward movement of said generally horizontalmember, for thereby imposing a side thrust on said vehicle.
 6. A deviceas recited in claim 5 in which for said means for discharging air fromsaid space laterally said generally horizontal member includes anupstanding flange on said outer edge thereof, said upstanding flangebeing normally in sealing relationship with said edge of said liftchamber, said upstanding flange being moved to a position where it isspaced downwardly from said edge of said lift chamber upon saidpredetermined downward movement of said generally horizontal member. 7.A device as recited in claim 4 including in addition a second diaphragminterconnecting said outer edge of said generally horizontal member andsaid edge of said lift chamber for substantially preventing lateraldischarge of air from said space upon downward movement of saidgenerally horizontal member.
 8. A device as recited in claim 7 in whichsaid opening means provides restricted communication between said liftchamber and said space, whereby air is substantially retained in saidspace and provides a springlike action and a damping effect uponoscillation of said generally horizontal member.
 9. In combination withan air-cushion vehicle having a lift chamber having an open bottom,means for providing pressurized air in said lift chamber, and agenerally rigid structure having a lateral surface spaced outwardly fromthe center of said lift chamber and extending along an edge of said liftchamber, a skirt arrangment for said lift chamber comprising a flexiblediaphragm disposed longitudinally of said edge so as to present one sideof said diaphragm adjacent said lift chamber, one longitudinal edge ofsaid diaphragm being attached to said vehicle adjacent said edge of saidlift chamber, a plate means, said plate means including an outer edgeconnected to the lower edge of said diaphragm, said plate means beinginclined downwardly from said outer edge thereof to a portion thereofwhich is beneath said lateral surface, said plate means including aninner edge spaced outwardly from the center of said lift chamber andadjacent said lateral surface for permitting air to flow from said liftchamber generally horizontally outwardly under said plate means to theexterior of said lift chamber, said plate means including a firstdownwardly and inwardly inclined portion, and a second generally flathorizontal portion connected to the lower edge of said first portion atan obtuse angle relative thereto and extending inwardly therefrom tosaid inner edge of said plate, for being reacted upon by pressures aboveand below said second portion for moving said skirt arrangement upwardlyand downwardly, means for applying pressurized air to the upper surfaceof said plate means and to said side of said flexible diaphragm, andflexible means interconnecting said plate means and said vehicle, saidplate means being a flexible sheet member, said means interconnectingsAid plate means and said vehicle including flexible elements attachedto said first portion and to said second portion of said plate means forgenerally maintaining the shape of said plate means when said platemeans is so subjected to pressure from pressurized air in said liftchamber.
 10. In combination with an air-cushion vehicle having a liftchamber having an open bottom, means for providing pressurized air insaid lift chamber, and a generally rigid structure having a lateralsurface spaced outwardly from the center of said lift chamber andextending along an edge of said lift chamber at the rearward endthereof, a skirt arrangement for said lift chamber comprising a flexiblediaphragm disposed longitudinally of said edge so as to present one sideof said diaphragm adjacent said lift chamber, one longitudinal edge ofsaid diaphragm being attached to said vehicle adjacent said edge of saidlift chamber, a plate means, said plate means including an outer edgeconnected to the lower edge of said diaphragm, said plate means beingincluded downwardly from said outer edge thereof to a portion thereofwhich is beneath said lateral surface, said plate means including aninner edge spaced outwardly from the center of said lift chamber andadjacent said lateral surface for permitting air to flow from said liftchamber generally horizontally outwardly under said plate means to theexterior of said lift chamber, said plate means being a substantiallyrigid member curved to form a shallow channel with a convex surfacefacing downwardly, said diaphragm being inclined downwardly andforwardly relative to said vehicle from said attachment thereof adjacentsaid edge of said lift chamber to said connection thereof to said platemeans, means for applying pressurized air to the upper surface of saidplate means and to said side of said flexible diaphragm, and flexiblemeans interconnecting said plate means and said vehicle.
 11. A device asrecited in claim 10 including in addition means for varying thedimension of said diaphragm for raising and lowering said plate means.12. A device as recited in claim 11 in which said means for varying thedimension of said diaphragm includes a rotatable spool on said vehicle,said one longitudinal edge of said diaphragm being attached to saidspool.
 13. A device as recited in claim 10 in which said substantiallyrigid member includes a portion inclined upwardly and forwardly relativeto said vehicle to an opposite edge thereof.
 14. A device as recited inclaim 10 in which said means interconnecting said plate means and saidvehicle includes a diaphragm inclined upwardly and forwardly from theforward edge of said substantially rigid member to said lateral surface,and including in addition a conduit means providing communicationbetween said lift chamber and the interior of said skirt arrangement,whereby pressurized air from said lift chamber inflates said skirtarrangement.
 15. In combination with an air-cushion vehicle having alift chamber having an open bottom, means for providing pressurized airin said lift chamber, and a generally rigid structure having a lateralsurface spaced outwardly from the center of said lift chamber andextending along an edge of said lift chamber, a skirt arrangement forsaid lift chamber comprising a flexible diaphragm disposedlongitudinally of said edge so as to present one side of said diaphragmadjacent said lift chamber, one longitudinal edge of said diaphragmbeing attached to said vehicle adjacent said edge of said lift chamber,a plate means, said plate means including an outer edge connected to thelower edge of said diaphragm, said plate means being inclined downwardlyfrom said outer edge thereof to a portion thereof which is beneath saidlateral surface, said plate means including an inner edge spacedoutwardly from the center of said lift chamber and adjacent said lateralsurface for permitting air to flow from said lift chamber generallyhorizontally outwardly under said plate means to the exterior of saidlift chamber, said plate means including a first downwardly and inwardlyinclined portion, and a second generally flat horizontal portionconnected to the lower edge of said first portion at an obtuse anglerelative thereto and extending inwardly therefrom to said inner edge ofsaid plate, for being reacted upon by pressures above and below saidsecond portion for moving said skirt arrangement upwardly anddownwardly, aperture means in said generally horizontal portion of saidplate means for discharging air from said skirt arrangement in agenerally downward direction adjacent said second portion andconstricting the outward generally horizontal flow of air from said liftchamber under said skirt arrangement, said aperture means including aduality of elongated slots, the first of said slots being adjacent theouter edge of said second portion and being inclined downwardly andinwardly for discharging a jet of air downwardly and inwardly therefrom,the second of said slots being inwardly of said first slot and beingsubstantially vertically oriented for discharging a jet of airvertically downwardly therefrom, means for applying pressurized air tothe upper surface of said plate means and to said side of said flexiblediaphragm, and flexible means interconnecting said plate means and saidvehicle.
 16. In combination with an air-cushion vehicle having a liftchamber having an open bottom, means for providing pressurized air insaid lift chamber, and a generally rigid structure having a lateralsurface spaced outwardly from the center of said lift chamber andextending along an edge of said lift chamber, a skirt arrangement forsaid lift chamber comprising a plurality of skirt units substantially inend-to-end alignment along said edge of said lift chamber, with the endsof adjacent skirt units being in juxtaposition, said skirt units beingunconnected to each other so as to be independently movable, each ofsaid skirt units including a flexible diaphragm disposed longitudinallyof said edge so as to present one side of said diaphragm adjacent saidlift chamber, one longitudinal edge of said diaphragm being attached tosaid vehicle adjacent said edge of said lift chamber, a plate means,said plate means including an outer edge connected to the lower edge ofsaid diaphragm, said plate means being inclined downwardly from saidouter edge thereof to a portion thereof which is beneath said lateralsurface, said plate means including an inner edge spaced outwardly fromthe center of said lift chamber and adjacent said lateral surface forpermitting air to flow from said lift chamber generally horizontallyoutwardly under said plate means to the exterior of said lift chamber,means for applying pressurized air to the upper surface of said platemeans and to said side of said flexible diaphragm, flexible meansinterconnecting said plate means and said vehicle, and an additionalflexible diaphragm at either end of said skirt unit positioned at theends of said first-mentioned diaphragm and the ends of said plate means,said additional flexible diaphragms covering less than the entire spaceat the ends of said skirt unit for allowing air to flow from one of saidskirt units to the other.
 17. In combination with an air-cushion vehiclehaving a lift chamber, means for providing pressurized air in said liftchamber, and a generally rigid structure having a lateral surfaceextending along an edge of said lift chamber, a skirt arrangement forsaid lift chamber comprising: a flexible diaphragm disposedlongitudinally of said edge so as to present one side of said diaphragmadjacent said lift chamber, one longitudinal edge of said diaphragmbeing attached to said vehicle adjacent said edge of said lift chamber,a plate means, said plate means including an edge connected to the loweredge of said diaphragm, a first portion extending downwardly andinwardly from said edge thereof with respect to said lift chamber, asecond generally horizontal portion beneath said lateral surfaceconnected to the lower edge of said first portion at an obtuse anglerelative thereto and extending inwardly therefrom with respect to saidlift chamber, and a third portion connected to the inner edge of saidfirst portion and extending upwardly and inwardly therefrom with respectto said lift chamber, said plate means including a duality of elongatedslots, the first of said slots extending longitudinally of said platemeans substantially at the connection between said first and secondportions thereof, the second of said slots extending longitudinally ofsaid plate means substantially at the connection between said second andthird portions thereof, said second portion of said plate means beingconnected to said third portion of said plate means so as to be pivotalrelative to said third portion of said plate means substantially aboutan axis extending generally along the line of connection between saidsecond and third portions, said first slot being defined on one sidethereof by the outer edge of said second portion of said plate means,means for so pivoting said second portion relative to said third portionfor increasing the size of said first slot, means for applyingpressurized air to the upper surface of said plate means and to saidside of said flexible diaphragm, and means interconnecting said platemeans and said vehicle, said means interconnecting said plate means andsaid vehicle being a second diaphragm, said second diaphragm extendingfrom said portion of said plate means to said generally rigid structure,said second diaphragm being connected to the inner edge of said thirdportion of said plate means.
 18. A device as recited in claim 17 inwhich for said connection of said second portion to said third portionthere are relatively narrow deflectable strips of said plate meansextending transversely across said second slot between said second andthird portions of said plate means.
 19. A device as recited in claim 18in which said first slot is inclined downwardly and inwardly relative tosaid vehicle, and said second slot is substantially vertical.
 20. Incombination with an air-cushion vehicle having a lift chamber having anopen bottom, means for providing pressurized air in said lift chamber,and a generally rigid structure having a lateral surface spacedoutwardly from the center of said lift chamber and extending along anedge of said lift chamber, a skirt arrangement for said lift chambercomprising a flexible diaphragm disposed longitudinally of said edge soas to present one side of said diaphragm adjacent said lift chamber, onelongitudinal edge of said diaphragm being attached to said vehicleadjacent said edge of said lift chamber, a plate means, said plate meansincluding an outer edge connected to the lower edge of said diaphragm,said plate means being inclined downwardly from said outer edge thereofto a portion thereof which is beneath said lateral surface, said platemeans including an inner edge spaced outwardly from the center of saidlift chamber and adjacent said lateral surface for permitting air toflow from said lift chamber generally horizontally outwardly under saidplate means to the exterior of said lift chamber, means for applyingpressurized air to the upper surface of said plate means and to saidside of said flexible diaphragm, flexible means interconnecting saidplate means and said vehicle, said flexible means being a seconddiaphragm extending from said portion of said plate means to saidgenerally rigid structure, said plate means including a first portionextending downwardly and inwardly with respect to said lift chamber, asecond generally horizontal portion conNected to the lower edge of saidfirst portion at an obtuse angle relative thereto and extending inwardlytherefrom with respect to said lift chamber, and a third portionconnected to the inner edge of said first portion and extending upwardlyand inwardly therefrom with respect to said lift chamber to said inneredge of said plate means, said second diaphragm being connected to theinner edge of said third portion of said plate means, said plate meansincluding a duality of elongated slots, the first of said slotsextending longitudinally of said plate means substantially at theconnection between said second and third portions thereof, said secondportion of said plate means being connected to said first portion ofsaid plate means so as to be pivotal relative to said first portion ofsaid plate means substantially about an axis extending generally alongthe line of connection between said first and second portions, saidsecond slot being defined on one side thereof by the inner edge of saidsecond portion of said plate means, and means for so pivoting saidsecond portion relative to said first portion for increasing the size ofsaid second slot.
 21. A device as recited in claim 20 in which for saidconnection of said second portion to said first portion there arerelatively narrow deflectable strips of said plate means extendingtransversely across said first slot between said first and secondportions of said plate means.
 22. A device as recited in claim 21 inwhich said second slot is inclined downwardly and inwardly relative tosaid vehicle, and said second slot is substantially vertical.